1. Technical Field
The present invention relates to a technique for detecting the surface of an object with fine asperity.
2. Related Art
Techniques for detecting a surface of an object with fine asperity, such as a human fingerprint, have been suggested. In JP-A-2004-317353, a detecting device in which multiple sensor circuits are arrayed in matrix along a contact surface of the object is disclosed. Here, each sensor circuit outputs a detection signal that is proportional to the distance between the contact surface and the object close thereto, or in contact therewith. With this structure, a comparator circuit is installed, and by analyzing the data output from the comparator circuit, the surface of the object is identified. Here, the comparator circuit outputs the data sets of two values, in accordance with a relationship between levels of a detection signal output from each sensor and a signal provided externally (hereafter referred to as “reference signals”).
However, detecting devices are subject to fluctuations in the electric characteristics (particularly threshold voltages) of the switching element that constitutes part of the device, such as the sensor circuit that generates the detection signals and the comparator circuit that compares the detection signals to the reference signals. Therefore, in order to perform detection evenly for every detecting device, a cumbersome operation is required by the user, including the adjustment of reference signal levels, while confirming the detected results by the detecting device.